The present invention relates to silane resins that can be structured (also referred to as organically modifiable (hetero) silicic acid poly condensates or organopolysiloxanes) that are reacted when exposed to radiation (in particular, in the UV range) or reacted thermally to inorganic-organic, O—Si—O group containing hybrid polymers with improved dielectric properties as well as excellent substrate adherence and, in particular, can be processed to structured layers. These materials are suitable for use in high and extremely high frequency ranges (for example, as multi-layer systems in SBU (sequential build-up) technology, in multi-layerthin-film circuits (TFC)). The invention further relates to a method for producing such silane resins. Finally, the invention relates to intermediates with which the aforementioned polymers can be produced, as well as a method for their preparation.
Polymers are used in various day-to-day applications well as in a series of high-tech uses (for example, information acquisition, information processing, and information transfer). Compared to purely organic polymers, organic-inorganic hybrid polymers, for example, those that are commercially available under the trademark ORMOCER® registered to the Fraunhofer Gesellschaft, exhibit in general excellent temperature resistance and thermal shape stability, excellent adherence to a plurality of materials, and many other beneficial properties. Such hybrid polymers are prepared in general by the so-called sol-gel process according to which the monomer or pre-condensed components (in general, optionally organo-modified silanes, partially in combination with additional metal-alkoxy compounds and/or other compounds) are subjected to hydrolysis and condensation of the appropriate groups. After removing, exchanging or supplementing the solvent that is present or the solvent that has been produced, a low viscosity to high viscosity resin or a lacquer is obtained that can be brought into a suitable form, for example, as a coating of substrate, as a shaped body, or as a diaphragm that, after shaping, can be dried, optionally can be cured further by polymerization of the organic groups that are present. The last-mentioned organic polymerization, if desired, can be realized only at predetermined locations, for example, for curing by selective irradiation by means of actinic radiation, wherein subsequently the material that has not been polymerized can be removed by means of suitable solvents. In this way, it is possible to obtain photo-lithographically structured three-dimensional bodies or surfaces. For example, DE 199 32 629 A1 discloses organo-modified silicic acid polycondensates that are stable under storage conditions, can be UV-cured and can be photo-structured; the polycondensates are transparent in the near infrared range (NIR). These resins can be used, for example, as a photoresist, as a photoresist with negative resist behavior, or as a dielectric (generally an insulating material) for Microsystems technology (includes inter alia microelectronics, microoptics, and micromechanics).
Support materials for thin film circuits are partially ceramic materials that are directly developed for hybrid applications; silicon wafers; or organic materials of the printed circuit board technology and semiconductor technology. Their dielectric or other properties, however, would not appear to make them useful in application in connection with the extremely high frequency range. For example, commercially available dielectrics (for example, benzocyclobutene: BCB such as Cyclotene™ 4026-46 of the Dow Chemical Company; polyimide PI: Pyraline™ 2722 of the DuPont Company; or glass fiber-reinforced PTFE laminate: RT/Duorid™ 5880 of the Rogers Corporation) exhibit good dielectric properties (for example, ∈Γ<3 and tan δ=40−8·10−3) within the low high frequency range (10 kHz). Moreover, with the aforementioned glass fiber reinforced PTFE laminate it has been shown also that attenuation values tan δ<3·10−3 in the lower extremely high frequency range at approximately 10 GHz can be obtained. The class of polyimides that can be structured by UV and the class of the benzocyclobutenes exhibit stability at higher temperatures but are designed only for thin film applications (processable film thickness for each layer ≦25 μm) and require curing conditions that must be critically reviewed in connection with sensitive components. A further disadvantage of these materials resides in that the adhesion strength varies greatly with the substrate properties and that these materials partially cannot be structured by means of conventional lithography. The high mechanical and thermal stability expected from the dielectric is not ensured when using such materials.
Inorganic-organic hybrid polymers containing O—Si—O groups are also suitable for use in the microelectronics industry. Resins and lacquers of such materials can have properties that enable their use as dielectrics in the low high frequency range. With them, it is possible to obtain, for example, dielectric constants of up to ∈Γ≈3 and dielectric loss of up to tan δ=4·10−3 at 10 kHz. For applications in high and extremely high frequency range the known materials are not useable however. For example, it was found that the UV-structured resins disclosed in the already mentioned DE 199 32 629 A1, which resins, because of their high transparency and good mechanical properties, would appear to be well suited for applications considered in the instant invention, exhibit significantly decreased values within the extremely high frequency range (in the GHz range). For example, a polymer of diphenyl silanediol and methacryloxy propyl trimethoxy silane in this range shows a loss of tan δ of 0.03. Accordingly, the application of such materials as a dielectric for extremely high frequency applications in communications technology (RF sending and receiving modules; multichip modules, MCM) or in the automobile industry (distance radar, multilayer thin/thick film circuits, TFC) has not been found to be satisfying up to now. This is so because such applications pose extreme requirements with regard to the properties of the dielectric in the microwave range, in particular, for frequencies between 10 and 100 GHz.
It Is an object of the present invention to provide materials whose dielectric properties within the high and extremely high frequency range (primarily between 10 and 100 GHz) are around ∈Γ<3 and tan δ<5·10−3 and which, moreover, have at least partially thermal, mechanical, and adhesive properties that exceed those of conventional, purely organic materials employed in extremely high frequency applications.
It has been surprisingly found that materials which are produced by employing a monomeric silanediol and at least one additional monomeric silane component and in which the silane component has at least one organically crosslinkable group that is bonded by carbon to the silicon atom, have the desired dielectric properties when the employed silanediol has no aryl group.
Preferably, the employed silanediol is an aliphatic silanediol whose organic rests preferably have a significant sterical requirement, for example, isobutyl, isopropyl, or cyclohexyl.
The other monomeric silane component is a compound with two or three groups which in the presence of hydroxy groups of the silanediol and optionally of a catalyst for condensation function as the leaving groups (they will be often referred to in the following only as “leaving groups” for reasons of simplification), for example, halogen; optionally substituted alkoxy, acyloxy, alkoxy carbonyl or NR3 with R3 equal hydrogen or lower alkyl. Alkoxy groups with particularly one up to four carbon atoms and lower alkyl groups of the same chain length are preferred. In principle, the leaving groups can also be OH groups. However, this is less favorable because the inorganic condensation reaction produces water that, in turn, can cause a reversibility of the reactions so that secondary reactions can no longer be excluded (see also infra). Moreover, the aforementioned silane component, as mentioned, has one or two organically crosslinkable groups that are stable with regard to hydrolysis and can be polymerized thermally and/or photo-chemically, for example, in the presence of UV photo-initiators. This group/these groups is/are bonded by a carbon to the silicon atom.
The aforementioned hybrid materials can be prepared by a single-step method wherein the reaction is carried out preferably in the absence of water. In this way, an unequivocal reaction route is forced. Secondary reactions are suppressed. By selecting suitable condensation catalysts and defined temperature ranges and reaction times, the reaction takes place within narrow stoichiometric limits when using the starting components in suitable quantitative ratios. Surprisingly, it was found that the selection of the condensation catalyst can be critical in some cases. In particular, the catalyst barium hydroxide proposed in DE 199 32 629 A1 is generally unsuitable. In contrast, good results can be obtained, for example, with ammonium fluorides, in particular, with tetrabutyl ammonium fluoride (in the form of the trihydrate). Because of the absence of water, the method reliably and reproducibly leads to products with the desired material properties such as viscosity, solubility, refractive index, substrate adhesion, temperature resistance, and dielectric properties. In particular, an excellent and unexpected temperature resistance is exhibited by the materials. The reproducibility of the course of the process is a prerequisite for the success of the plurality of process steps that are required for the photo-lithographic structure generation (application method, for example, by spin-casting (“spin on”); pre-treatments such as pre-drying or pre-curing; photo polymerization; intermediate treatment, for example, postexposure bake; development; post treatment, for example, post baking), and thus for the use in the microsystems technology and for the reliability of the component that is finally produced.
In Chemical Abstracts 1996, 127:293965 the kinetics of the photochemical polymerization of the reaction product of methacrylic acid (dihydroxy-methyl-silyl) methylester with dimethyl silanediol was examined. This reaction product and its polymerized product are not encompassed by the present invention.
The present invention moreover provides a new method with which the silanediols to be used as a starting material can be produced. This method enables the gentle preparation of silanediols in a reliable and reproducible yield; this has been a problem in the past because of possible secondary reactions (further reaction to polymer products). Also, previously unknown silanediols that are well suited as starting materials for the silane resin according to the invention can be prepared by this method.